The present invention relates to a motor vehicle accessory to be applied to a tire of the motor vehicle in order to interpose a resistance against rotation of the tire on the ground. The invention is therefore particularly useful as a locking device for protecting the vehicle against theft. The invention, however, may also be used in a manner similar to the well known "Denver Boot", as a locking device for immobilizing a vehicle illegally parked in a restricted area, requiring the owner to pay a fine for removal of the device. Still further uses of the accessory of the present invention include as an aid in extricating a motor vehicle from sand, mud, snow or ice, or in converting the vehicle tires to snow tires for driving under snow-covered or ice-covered roads.